Acid-catalyzed hydrocarbon conversion process

ABSTRACT

Substitution of aluminum or gallium for boron or iron contained in the framework of a high silica content zeolite is effected by treating the zeolite in liquid water in the presence of a compound of aluminum or gallium. Catalyst comprising the treated zeolite is used for conducting acid-catalyzed reactions of organic compounds, e.g. cracking of hydrocarbon compounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 713,213, filedMar. 18, 1985, now abandoned, which is a continuation-in-part ofapplication Ser. No. 631,688, filed July 16, 1984, now U.S. Pat. No.4,524,140, which is a continuation-in-part of application Ser. No.465,987, filed Feb. 14, 1983, now U.S. Pat. No. 4,513,091, the entirecontent of each being herein incorporated by reference.

FIELD OF THE INVENTION

This invention relates to acid catalysis, e.g. cracking, of organiccompound feedstock over catalyst material treated in a special way forincreasing the acid catalytic activity thereof. In particular, a novelcatalyst activation process is followed to enhance the alpha value ofhigh-silica zeolite catalyst by hydrothermal treatment in contact withan inorganic activating agent.

BACKGROUND OF THE INVENTION

Zeolite catalysts have become widely used in the processing of petroleumand in the production of various petrochemicals. Reactions such ascracking, hydrocracking, catalytic dewaxing, alkylation, dealkylation,transalkylation, isomerization, polymerization, addition,disproportionation and other acid catalyzed reactions may be performedwith the aid of these catalysts. Certain natural and synthetic zeolitesare known to be active for reactions of these kinds.

The common crystalline zeolite catalysts are the aluminosilicates suchas Zeolites A, X, Y and mordenite. Structurally each such material canbe described as a robust three dimensional framework by SiO₄ and AlO₄tetrahedra that is crosslinked by the sharing of oxygen atoms wherebythe ratio of total aluminum and silicon atoms to oxygen is 1:2. Thesestructures (as well as others of catalytic usefulness) are porous, andpermit access of reactant molecules to the interior of the crystalthrough windows formed of eight-membered rings (small pore) or oftwelve-membered rings (large pore). The electrovalence of the aluminumthat is tetrahedrally contained in the robust framework is balanced bythe inclusion of cations in the channels (pores) of the crystal.

An "oxide" empirical formula that has been used to describe the aboveclass of crystalline zeolites is

    M.sub.2/n O.Al.sub.2 O.sub.3.xSiO.sub.2.yH.sub.2 O

wherein M is a cation with valence n, x has a value of from 2 to 10, andy has a value which varies with the pore volume of the particularcrystal under discussion. The above oxide formula may be rewritten as ageneral "structural" formula

    M.sub.2/n (AlO.sub.2.wSiO.sub.2)yH.sub.2 O

wherein M and y are defined as above, and wherein w has a value from 1to 5. In this representation, the composition of the robust framework iscontained within the parenthesis, and the material (cations and water)contained in the channels is outside the parenthesis. One skilled in theart will recognize that x in the empirical oxide formula represents themole ratio of silica to alumina in the robust framework of a crystallinezeolite, and shall be referred to herein simply by the expression incommon usage, i.e. "the silica to alumina ratio". (See "ZeoliteMolecular Sieves", Donald W. Breck, Chapter One, John Wiley and Sons,New York, N.Y. 1974, which is incorporated herein by reference asbackground material).

With few exceptions, such as with Zeolite A wherein x=2, there are feweralumina tetrahedra than silica tetrahedra in the robust framework. Thus,aluminum represents the minor tetrahedrally coordinated constituent ofthe robust framework.

It is generally recognized that the composition of the robust frameworkmay be varied within relatively narrow limits by changing the proportionof reactants, e.g., increasing the concentration of the silica relativeto the alumina in the zeolite synthesis mixture. However, definitelimits in the maximum obtainable silica to alumina ratio are observed.For example, synthetic faujasites having a silica to alumina ratio ofabout 5.2 to 5.6 can be obtained by changing said relative proportions.However, if the silica proportion is increased above the level whichproduces the 5.6 ratio, no commensurate increase in the silica toalumina ratio of the crystallized synthetic faujasite is observed. Thus,the silica to alumina ratio of about 5.6 must be considered an upperlimit in a preparative process using conventional reagents.Corresponding upper limits in the silica to alumina ratio of mordeniteand erionite via the synthetic pathway are also observed. It issometimes desirable to obtain a particular zeolite, for any of severalreasons, with a higher silica to alumina ratio than is available bydirect synthesis. U.S. Pat. No. 4,273,753 to Chang and the referencescontained therein describe several methods for removing some of thealuminum from the framework, thereby increasing the silica to aluminaratio of a crystal.

For the above zeolite compositions, wherein x has a value of 2 to 10, itis known that the ion exchange capacity measured in conventional fashionis directly proportional to the amount of the minor constituent in therobust framework, provided that the exchanging cations are not so largeas to be excluded by the pores. If the zeolite is exchanged withammonium ions and calcined to convert it to the hydrogen form, itacquires a large catalytic activity measured by the alpha activity test,which test is more fully described below. And, the ammonium form of thezeolite desorbs ammonia at elevated temperature in a characteristicfashion.

Synthetic zeolites wherein x is greater than 12, which have little orsubstantially no aluminum content, are known. Such zeolites have manyimportant properties and characteristics and a high degree of structuralstability such that they have become candidates for use in variousprocesses including catalytic processes. Materials of this type areknown in the art and include high silica content aluminosilicates, suchas ZSM-5 (U.S. Pat. No. 3,702,886), ZSM-11 (U.S. Pat. No. 3,709,979),and ZSM-12 (U.S. Pat. No. 3,832,449) to mention a few. Unlike thezeolites described above wherein x=2 to 5, the silica to alumina ratiofor at least some of the high silica content zeolites is unbounded.ZSM-5 is one such example wherein the silica to alumina ratio is atleast 12. U.S. Pat. No. 3,941,871 discloses a crystalline metalorganosilicate essentially free of aluminum and exhibiting an X-ray ofdiffraction pattern characteristic of ZSM-5. U.S. Pat. Nos. 4,061,724,4,073,865 and 4,104,294 describe microporous crystalline silicas ororganosilicates wherein the alumina content present is at very lowlevels. Some of the high silica content zeolites contain boron or ironwhich is not reversibly removed by simple ion exchange, i.e. thezeolites contain tenaciously bound boron or iron.

Because of the extremely low alumina content of certain high silicacontent zeolites, there catalytic activity is not as great as materialswith a higher alumina content. Therefore, when these materials arecontacted with an acidic solution and thereafter are processed in aconventional manner, they are not as catalytically active foracid-catalyzed reaction as their higher alumina content counterparts.

In U.S. Pat. Nos. 3,960,978 and 4,021,502, Plank, Rosinski and Givensdisclose conversion of C₂ -C₅ olefins, alone or in admixture withparaffinic components, into higher hydrocarbons over crystallinezeolites having controlled acidity. Garwood et al. have also contributedprocessing techniques for conversion of olefins to gasoline anddistillate, as in U.S. Pat. Nos. 4,150,062, 4,211,640 and 4,227,992.

A number of U.S. patents teach heteroatom feed conversion. Examples ofthese are U.S. Pat. Nos. 3,894,104, 3,894,106, 3,894,107, 3,899,544,3,965,205, 4,046,825, 4,156,698 and 4,311,865. Methanol is converted togasoline in U.S. Pat. Nos. 4,302,619, 3,928,483 and 4,058,576 asexamples. Methanol is converted to olefins and/or aromatics in, forexample, U.S. Pat. Nos. 3,911,041, 4,025,571, 4,025,572, 4,025,575 and4,049,735.

U.S. Pat. No. 4,380,685 teaches para-selective alkylation,transalkylation or disproportionation of a substituted aromatic compoundto form a dialkylbenzene compound mixture over catalyst comprisingzeolite characterized by a constraint index 1 to 12 and a silica:aluminamole ratio of at least 12:1, the catalyst having thereon incorporatedvarious metals and phosphorus. Other patents covering alkylation andtransalkylation include U.S. Pat. Nos. 4,127,616, 4,361,713, 4,365,104,4,367,359, 4,370,508 and 4,384,155. Toluene is converted to para-xylenein U.S. Pat. Nos. 3,965,207, 3,965,208, 3,965,209, 4,001,346, 4,002,698,4,067,920, 4,100,215 and 4,152,364, to name a few. Alkylation witholefins is taught, for example, in U.S. Pat. Nos. 3,962,364 and4,016,218 and toluene is disproportionated in, for example, U.S. Pat.Nos. 4,052,476, 4,007,231, 4,011,276, 4,016,219 and 4,029,716.Isomerization of xylenes is taught in, for example, U.S. Pat. Nos.4,100,214, 4.101,595, 4,158,676, 4,159,282, 4,351,979, 4,101,597,4,159,283, 4,152,363, 4,163,028, 4,188,282 and 4,224,141.

SUMMARY OF THE INVENTION

A unique crystalline zeolite material having enhanced acid activity(alpha-value) has been discovered by the technique of hydrothermallytreating, in the presence of a compound of aluminum or gallium, a highsilica content zeolite that contains tenaciously held boron or iron toeffect substitution by aluminum or gallium for said boron or iron. Theuse of this material as catalyst for acid-catalyzed chemical reactionsis the object of the present invention.

The activity enhancing technique is particularly advantageous fortreating hydrogen form or ammonium form zeolites that have a silica toalumina ratio greater than 100 to 1, and that have a boron or ironcontent of at least 0.1 wt%.

The novel process of this invention permits the use of high silicacontent zeolites which have all the desirable properties inherentlypossessed by such high silica materials, and yet have an acid activity(alpha-value) which heretofore has only been possible to achieve withmaterials having a higher aluminum content in the robust framework.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of alpha values v. boron contents, in weight percent,of crystalline zeolites of Examples 2-16.

FIG. 2 shows temperature programmed desorption thermograms, comparingthe Example 7 zeolite with the Example 16 zeolite.

DESCRIPTION OF PREFERRED EMBODIMENTS

As has heretofore been stated, the novel catalyst for use in the processof this invention involves a changed composition of the robust frameworkof a high silica content zeolite that initially contains at least 0.1wt% of tenaciously held boron or iron. The expression "high silicacontent" is intended herein to define a crystalline zeolite structurewhich has a silica to alumina ratio greater than 20 and more preferablygreater than 100, up to and including those highly siliceous materialswhere the silica to alumina ratio is very large, e.g. greater than 1000.This latter group of highly siliceous materials is exemplified by U.SPat. Nos. 3,941,871, 4,061,724, 4,073,865 and 4,104,294 wherein thematerials are prepared from forming solutions to which no deliberateaddition of aluminum was made. However, trace quantities of aluminum arepresent due to the impurity of the reactant solutions.

The preferred high silica content zeolite that is to be activated by theprocess of this invention has the crystal structure of an intermediatepore size zeolite, such as ZSM-5, evidenced by X-ray diffraction and"Constraint Index". This type of zeolite freely sorbs normal hexane, andhas a pore size intermediate between the small pore zeolites such asLinde A and the large pore zeolites such as Linde X, the pore windows inthe crystals being formed of 8-membered rings. The crystal frameworkdensities of this type zeolite in the dry hydrogen form is not less than1.6 grams per cubic centimeter. It is known that such zeolites exhibitconstrained access to singly methyl-branched paraffins, and that thisconstrained access can be measured by cracking a mixture of n-hexane and3-methylpentane and deriving therefrom a Constraint Index, as describedin U.S. Pat. No. 4,231,899, incorporated herein by reference as to thatdescription. Such zeolites exhibit a Constraint Index of 1 to 12provided they have sufficient catalytic activity or are activated by themethod of this invention to impart such activity. The boron containingand iron containing intermediate pore zeolites useful for the process ofthis invention are those having a crystal structure exemplified byZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and ZSM-48. Column 4, line30 to column 11, line 26 inclusive of U.S. Pat. No. 4,385,195 issued May24, 1983, and the U.S. Patents referred to therein, are incorporatedherein by reference for a detailed description including the X-raydiffraction patterns of the foregoing zeolites; a detailed descriptionof crystal density and method for measuring this property; a detaileddescription of Constraint Index and method for measuring this property;and, for matter related to the foregoing.

Methods for preparing high silica content zeolites that containtenaciously held boron or iron are known in the art and are notconsidered part of the present invention. The amount of boron containedtherein, for example, may be made to vary by incorporating differentamounts of borate ion in, for example, a ZSM-5 forming solution. Onesuch recipe is shown, for example, by Example 6 of European Patent68,796. Prior to activation by treatment with aluminum or gallium by themethod of this invention, the chosen zeolite is calcined and convertedby ion exchange to the ammonium or to the hydrogen form by calcination,by methods known to those skilled in the art. Although either theammonium or the hydrogen form may be activated, the hydrogen form ispreferred since it is somewhat more effective. For purposes of thepresent invention, the zeolite must contain at least about 0.1 wt% boronor iron, although it may contain from 0.1 wt % to about 2.5 wt%. Ingeneral, under comparable conditions, the higher the initial content oftenaciously held boron or iron, the greater the degree of substitutionand of enhancement of catalytic activity.

The ammonium or hydrogen form of the high silica content zeolite istreated in a liquid water medium with a source of aluminum or gallium toinduce substitution and activation. The treatment is conducted at anelevated temperature of about 50° C. to 375° C. under ambient orautogenous pressure so as to maintain the water in liquid phase, and fora time effective to induce the desired extent of substitution. Dependingon the nature of the aluminum or gallium source, and depending on thetemperature, effective substitution is achieved in from about 0.25 to150 hours.

Although aluminum or gallium salts such as chlorides, sulfates andnitrates may be used, it is preferred to use the solid chalcogenides ofthese metals. Particularly useful are the various sesquioxides, such asalpha alumina monohydrate, and gel precursors of the sesquioxides. Thesolid oxide may be in the form of distinct particles, or it may becomposited with the zeolite as binder. For purposes of the presentinvention, the preferred treating material is aluminum in the form of asolid oxide and a particularly preferred embodiment is the use of alphaalumina monohydrate binder, composited with the zeolite to be treated.In general, a large excess of the treating material is used to effectthe substitution.

In general, after completion of the substitution treatment, it isdesirable to convert the treated zeolite to the hydrogen form, such asby ion exchange and/or calcination, prior to use of the product ascatalyst.

While not wishing to be bound by theory, it is believed that theeffectiveness of this invention is a result of the substitution ofaluminum or gallium for boron or iron contained in the robust frameworkof the zeolite catalyst. Whereas either framework boron, for example, orframework aluminum, would be expected (if in the trivalent state) to beassociated with interstitial cations such as hydrogen ions, thoseassociated with boron have a very low or an undetectable catalyticactivity for cracking n-hexane under conditions at which hydrogen ionsassociated with aluminum have a very large activity. As is known in theart, the acid catalytic activity of a zeolite may be measured by its"alpha value," which is the ratio of the rate constant of a test samplefor cracking normal hexane to the rate content of a standard referencecatalyst. Thus, an alpha value=1 means that the test sample and thestandard reference have about the same activity. The alpha test isdescribed in U.S. Pat. No. 3,354,078 and in the The Journal ofCatalysis, Vol. IV, pp. 527-529 (August 1965), each incorporated hereinas to that description. The relationship of alpha value to the intrinsicrate constants of other acid-catalyzed reactions is detailed in Nature,Vol. 309, pp. 589-591, 14 June 1984, incorporated herein by reference asto that detail.

In general, organic compounds such as, for example, those selected fromthe group consisting of hydrocarbons, alcohols and ethers, are convertedto conversion products such as, for example, aromatics and lowermolecular weight hydrocarbons, by way of the present process by contactunder organic compound conversion conditions including a temperature offrom about 100° C. to about 800° C., a pressure of from about 0.1atmosphere (bar) to about 200 atmospheres, a weight hourly spacevelocity of from about 0.08 hr⁻¹ to about 2000 hr⁻¹ or a liquid hourlyspace velocity of from about 0.5 hr⁻¹ to about 100 hr⁻¹, and ahydrogen/feedstock organic, e.g., hydrocarbon, compound mole ratio offrom 0 (no added hydrogen) to about 100.

Such conversion processes include, as a non-limiting example, crackinghydrocarbons to lower molecular weight hydrocarbons with reactionconditions preferably including a temperature of from about 300° C. toabout 800° C., a pressure of from about 0.1 atmosphere (bar) to about 35atmospheres and a weight hourly space velocity of from about 0.1 hr⁻¹ toabout 20 hr⁻¹.

As will be seen in the examples which follow, although the method ofthis invention results in some increase in catalytic activity even whenno boron is present, the presence of increasing amounts of tenaciouslybound boron results in progressively larger increases of acid activity.These examples are for the purpose of illustrating this invention, andare not intended to limit the scope thereof, which scope is defined bythis entire specification including the claims appended thereto. Allparts and proportions are by weight unless explicitly stated to beotherwise. All alpha values reported in these examples refer tomeasurements made with the sample in the hydrogen form.

EXAMPLE 1

A high silica content ZSM-5 that contained tenaciously held boron wasprepared by the method described in U.S. Pat. No. 4,269,813. A portionof the product was evaluated for acid activity and was found to have analpha value of 7.

Another portion of the product was converted to the hydrogen form andmixed with an equal part of gamma-alumina beads. The mixture washydrothermally treated in liquid water at 205° C. for 18 hours. Theproduct zeolite was separated from the beads, ammonium exchanged andcalcined. Its alpha value was found to be 12.

EXAMPLES 2-7

Six different ZSM-5 preparations with a low content of alumina weremade. They were prepared to contain from 0 wt% up to 0.95 wt% boron.Each of the products was found to have the X-ray diffraction pattern ofZSM-5.

A portion of each of the products was analyzed for aluminum and boroncontent. The results were summarized in Table 1. The alpha values ofthese materials before hydrothermal treatment was shown in FIG. 1.

                  TABLE 1                                                         ______________________________________                                        Example        Al, ppm  B, wt %                                               ______________________________________                                        2              677      0.00                                                  3              640      0.37                                                  4              604      0.42                                                  5              527      0.54                                                  6              670      0.58                                                  7              600      0.95                                                  ______________________________________                                    

EXAMPLES 8-11

Portions of the products of Examples 2, 5, 6 and 7, respectively, werecalcined in air and base exchanged with ammonium acetate solution toconvert to the ammonium form. Each sample was then placed in a 30 mlscrew-cap Oak Ridge type teflon centrifuge tube, and an equal weight of1.5 mm gamma alumina beads was added. The samples were covered withabout 20 ml of water and placed in a 500 ml Autoclave EngineersZipperclave with stirrer removed, and heated to 155° C. for 65 hoursunder autogeneous pressure. The zeolite crystals were separated from thealumina beads, exchanged with 1N NH₄ NO₃ at 25° C. for 18 hours, washedwith distilled water and calcined at 538° C. for 30 minutes. Thezeolites were then tested for acid activity using the alpha test.Results are summarized in FIG. 1, which plots alpha vs. wt% B (boron) inthe parent material.

EXAMPLES 12-16

Portions of each of the products of Examples 2, 3, 4, 6, and 7 weretaken to provide materials for Examples 12-16, respectively, thencalcined in air, converted to the ammonium form and calcined to convertthe ammonium form to the hydrogen form.

The hydrogen form samples were treated in the same manner as describedfor Examples 8-11, and the alpha values determined. The results areshown in FIG. 1, in increasing order of boron content of the parentmaterials.

EXAMPLE 17

Portions of the products of Examples 7 and 16 were converted to theammonium form and subjected to temperature-programmed desorption. Theresults are shown in FIG. 2.

As shown in the drawing, the untreated sample that contained boronexhibits only low-temperature desorption, ascribable to framework boron,while the treated sample shows a large high-temperature peak, ascribableto framework aluminum, and a small low-temperature peak ascribable toresidual framework boron.

EXAMPLE 18

A portion of the product of Example 7 was treated as in Example 16,except that a saturated aqueous gallium chloride solution was usedinstead of the alumina beads. The product, in the hydrogen form, wasfound to have an alpha value above 330.

What is claimed is:
 1. A process for converting a feedstock comprisinghydrocarbon compounds to conversion product comprising hydrocarboncompounds of lower molecular weight than feedstock hydrocarbon compoundswhich comprises contacting said feedstock at conditions sufficient toconvert said feedstock to said products with a catalyst compositionprepared by a method for substituting aluminum or gallium for boron oriron contained in the robust framework of a high silica contentcrystalline zeolite, which method comprises hydrothermally treating saidzeolite in the presence of a compound of said aluminum or gallium, saidhydrothermal treatment being under conditions effective to induce saidsubstitution.
 2. The process of claim 1 wherein said aluminum or galliumcompound is water soluble.
 3. The process of claim 1 wherein saidaluminum or gallium compound is an oxide.
 4. The process of claim 3wherein said aluminum compound is an oxide binder composited with saidzeolite.
 5. The process of claim 1 wherein said high silica contentcrystalline zeolite has the structure of ZSM-5, ZSM-11, ZSM-12, ZSM-23,ZSM-35, ZSM-38 or ZSM-48.
 6. The process of claim 4 wherein said oxidebinder is alumina.
 7. The process of claim 5 wherein said zeolite hasthe structure of ZSM-5.
 8. The process of claim 6 wherein said zeolitehas the structure of ZSM-5.
 9. The process of claim 1 wherein saidhydrothermal treatment conditions include a temperature of from about50° C. to about 375° C.
 10. A process for converting a feedstockcomprising hydrocarbon compounds to conversion product comprisinghydrocarbon compounds of lower molecular weight than feedstockhydrocarbon compounds which comprises contacting said feedstock atconditions sufficient to convert said feedstock to said products with acatalyst composition prepared by a method for substituting aluminum orgallium for boron or iron contained in the robust framework of a highsilica content crystalline zeolite having the structure of ZSM-5, whichmethod comprises hydrothermally treating said zeolite in the presence ofa compound of said aluminum or gallium, said hydrothermal treatmentbeing under conditions effective to induce said substitution.
 11. Theprocess of claim 10 wherein said aluminum or gallium compound is watersoluble.
 12. The process of claim 10 wherein said aluminum or galliumcompound is an oxide.
 13. The process of claim 12 wherein said aluminumcompound is an oxide binder composited with said zeolite.
 14. Theprocess of claim 13 wherein said oxide binder is alumina.
 15. Theprocess of claim 1 wherein said conversion conditions include atemperature of from about 100° C. to about 800° C., a pressure of fromabout 0.1 atmosphere to about 200 atmospheres, a weight hourly spacevelocity of from about 0.08 hr⁻¹ to about 2000 hr⁻¹ and ahydrogen/feedstock hydrocarbon mole ratio of from 0 to about
 100. 16.The process of claim 15 wherein said conversion conditions include atemperature of from about 300° C. to about 800° C., a pressure of fromabout 0.1 atmosphere to about 35 atmospheres and a weight hourly spacevelocity of from about 0.1 hr⁻¹ to aout 20 hr⁻¹.
 17. The process ofclaim 10 wherein said conversion conditions include a temperature offrom about 100° C. to about 800° C., a pressure of from about 0.1atmosphere to about 200 atmospheres, a weight hourly space velocity offrom about 0.08 hr⁻¹ to about 2000 hr⁻¹ and a hydrogen/feedstockhydrocarbon mole ratio of from 0 to about
 100. 18. The process of claim17 wherein said conversion conditions include a temperature of fromabout 300° C. to about 800° C., a pressure of from about 0.1 atmosphereto about 35 atmospheres and a weight hourly space velocity of from about0.1 hr⁻¹ to aout 20 hr⁻¹.